In order to avoid such disturbances, certain technical steps are required, as described in German Offenlegungsschrift No. 26 49 886, where the individual lenses of the lens array are made of individual components which, in addition, contain the respective allocated aperture.
On the other hand, a solar collector has become known from German Offenlegungsschrift No. 26 31 412 where it is not necessary to execute a tracking movement of the entire solar collector; there, mechanical controls are provided which permit the positioning of the lenses as a function of the position of the sun. However, the invention does not comprise an automatic tracking of the position of the sun; this positioning has to be done manually or, as specified in German Offenlegungsschrift No. 25 11 740, by means of a time control for approximately ensuring the nominal position of the radiation-collecting elements. A master control directly ruled by sun radiation can execute the precise positioning of the angular position.
It can, therefore, be concluded that an ideal solar collector should have an automatic sun tracking device, also because of the seasonal adjustment and that, as specified in German Auslegungsschrift No. 25 45 224, selectively reflecting layers are associated with the absorber in such a manner that the solar radiation is sufficiently absorbed, and that long-wave infrared, on the other hand, is only slightly reemitted. The above specified arrangements, however, do not simultaneously satisfy all these demands, mainly because the tracking for the purpose of collecting the radiation independently of the respective sun position requires on the one hand complicated control mechanisms and can on the other be automatically realized under certain conditions only.
It is, therefore, the object of the invention to provide a solar collector which automatically tracks the respective position of the sun in a manner sufficing for practical application, said collector acting also as a black body.
This object is achieved according to the invention, as specified, by providing a structure where the radiation passages are enabled by the focused light energy.
There exist several possibilities of providing free light passages, owing to the focusing energy, in a layer having a reflecting back. An arrangement preferred in accordance with the invention provides that the radiation passages are enabled in a scale coating provided in the focal plane and composed of individual bimetallic scales that are bendable under the influence of radiation focused thereon, said scale coating provided in the focal plane of light-focusing components and arranged on a dielectric substrate is known per se from IBM Technical Disclosure Bulletin, Vol. 13, No. 3, August 1970, pages 603 and 604, but contrary to that invention the metallic scales there can be bent under the influence of Coulomb forces so that light focused thereon is reflected at respective different angles, depending on whether or not the respective metallic scale involved is bent.
Since bimetallic scales can easily be made in minimum size, an advantageous development of the invention provides that the dimensions of the bimetallic scales are selected in such a manner that a number in the order of 100 bimetallic scales are allocated to each lens of the lens array.
For simplifying production, it would be advisable to provide the scale coating on a substrate which also forms the lens array plate so that the refractive index and lens radius for providing the necessary focal plane are thus advantageously adapted to each other.
In order to avoid an unnecessary heating of the bimetallic scale coating in operation, it can, on the other hand, also be quite advantageous for design reasons to provide a space between substrate and lens array, and to direct through that space, a cooling medium which can be either a gas or another fluid, depending on the kind of solar collector operation. In that case, however, the refractive indices of substrate, lens array plate and cooling medium should correspond, if possible.
According to another aspect of the invention, the bimetallic scale coating contains as bimetallic scales relatively short copper lamellae and relatively long aluminum lamellae provided by means of welding or soldering on several aluminum strips vapor-deposited process taking place by means of conventional mask processes. Equally arranged aluminum strips are vapor-deposited on a glass substrate. Both groups of aluminum strips are connected at their ends to transversal aluminum strips which, when the synthetic material support is superimposed with the glass substrate in such a manner that the aluminum strips are placed one over the other, are used as current connectors in insulation from each other, for the subsequent welding of the aluminum strips superimposed upon each other, and for their simultaneous pressing together. This electric welding is thus performed under the influence of pressure in that, e.g., a roller is moved over the synthetic material substrate transversally to the aluminum strips so that the strips are welded to each other point-by-point. Subsequently, the synthetic material support is removed by means of an organic solvent.
The method as disclosed by the invention can be modified in such a manner that prior to the removal of the synthetic material support, the aluminum strips of the synthetic material support are welded to those of the glass substrate by means of a laser beam welding process as described for some other purpose in German Offenlegungsschrift No. 21 39 850.